/// <summary>
/// Gets Besselian elements values for specified Juluan Day.
/// </summary>
/// <param name="jd">Julian Day of interest</param>
/// <returns></returns>
internal InstantBesselianElements GetInstantBesselianElements(double jd)
{
//if (jd < From || jd > To)
// throw new ArgumentException($"Polynomial Besselian elements valid only for Julian Day in range [{From} ... {To}].", nameof(jd));
// difference, with t0, in step units
double t = (jd - JulianDay0) / Step;
return(new InstantBesselianElements()
{
X = X.Select((x, n) => x * Pow(t, n)).Sum(),
Y = Y.Select((y, n) => y * Pow(t, n)).Sum(),
L1 = L1.Select((l1, n) => l1 * Pow(t, n)).Sum(),
L2 = L2.Select((l2, n) => l2 * Pow(t, n)).Sum(),
D = D.Select((d, n) => d * Pow(t, n)).Sum(),
Mu = To360(Mu.Select((mu, n) => mu * Pow(t, n)).Sum()),
F1 = F1.Select((f1, n) => f1 * Pow(t, n)).Sum(),
F2 = F2.Select((f2, n) => f2 * Pow(t, n)).Sum(),
dX = Derivative(X, t),
dY = Derivative(Y, t),
dL1 = Derivative(L1, t),
dL2 = Derivative(L2, t),
dD = Derivative(D, t),
dMu = Derivative(Mu, t)
});
}